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<div class="section" id="angle-style-dipole-command">
<span id="index-0"></span><h1>angle_style dipole command</h1>
</div>
<div class="section" id="angle-style-dipole-omp-command">
<h1>angle_style dipole/omp command</h1>
<div class="section" id="syntax">
<h2>Syntax</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">angle_style</span> <span class="n">dipole</span>
</pre></div>
</div>
</div>
<div class="section" id="examples">
<h2>Examples</h2>
<div class="highlight-default"><div class="highlight"><pre><span></span><span class="n">angle_style</span> <span class="n">dipole</span>
<span class="n">angle_coeff</span> <span class="mi">6</span> <span class="mf">2.1</span> <span class="mf">180.0</span>
</pre></div>
</div>
</div>
<div class="section" id="description">
<h2>Description</h2>
<p>The <em>dipole</em> angle style is used to control the orientation of a dipolar
atom within a molecule <a class="reference internal" href="#orsi"><span class="std std-ref">(Orsi)</span></a>. Specifically, the <em>dipole</em> angle
style restrains the orientation of a point dipole mu_j (embedded in atom
&#8216;j&#8217;) with respect to a reference (bond) vector r_ij = r_i - r_j, where &#8216;i&#8217;
is another atom of the same molecule (typically, &#8216;i&#8217; and &#8216;j&#8217; are also
covalently bonded).</p>
<p>It is convenient to define an angle gamma between the &#8216;free&#8217; vector mu_j
and the reference (bond) vector r_ij:</p>
<img alt="_images/angle_dipole_gamma.jpg" class="align-center" src="_images/angle_dipole_gamma.jpg" />
<p>The <em>dipole</em> angle style uses the potential:</p>
<img alt="_images/angle_dipole_potential.jpg" class="align-center" src="_images/angle_dipole_potential.jpg" />
<p>where K is a rigidity constant and gamma0 is an equilibrium (reference)
angle.</p>
<p>The torque on the dipole can be obtained by differentiating the
potential using the &#8216;chain rule&#8217; as in appendix C.3 of
<a class="reference internal" href="pair_gayberne.html#allen"><span class="std std-ref">(Allen)</span></a>:</p>
<img alt="_images/angle_dipole_torque.jpg" class="align-center" src="_images/angle_dipole_torque.jpg" />
<p>Example: if gamma0 is set to 0 degrees, the torque generated by
the potential will tend to align the dipole along the reference
direction defined by the (bond) vector r_ij (in other words, mu_j is
restrained to point towards atom &#8216;i&#8217;).</p>
<p>The dipolar torque T_j must be counterbalanced in order to conserve
the local angular momentum. This is achieved via an additional force
couple generating a torque equivalent to the opposite of T_j:</p>
<img alt="_images/angle_dipole_couple.jpg" class="align-center" src="_images/angle_dipole_couple.jpg" />
<p>where F_i and F_j are applied on atoms i and j, respectively.</p>
<p>The following coefficients must be defined for each angle type via the
<a class="reference internal" href="angle_coeff.html"><span class="doc">angle_coeff</span></a> command as in the example above, or in
the data file or restart files read by the <a class="reference internal" href="read_data.html"><span class="doc">read_data</span></a>
or <a class="reference internal" href="read_restart.html"><span class="doc">read_restart</span></a> commands:</p>
<ul class="simple">
<li>K (energy)</li>
<li>gamma0 (degrees)</li>
</ul>
<hr class="docutils" />
<p>Styles with a <em>gpu</em>, <em>intel</em>, <em>kk</em>, <em>omp</em>, or <em>opt</em> suffix are
functionally the same as the corresponding style without the suffix.
They have been optimized to run faster, depending on your available
hardware, as discussed in <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a>
of the manual. The accelerated styles take the same arguments and
should produce the same results, except for round-off and precision
issues.</p>
<p>These accelerated styles are part of the GPU, USER-INTEL, KOKKOS,
USER-OMP and OPT packages, respectively. They are only enabled if
LAMMPS was built with those packages. See the <a class="reference internal" href="Section_start.html#start-3"><span class="std std-ref">Making LAMMPS</span></a> section for more info.</p>
<p>You can specify the accelerated styles explicitly in your input script
by including their suffix, or you can use the <a class="reference internal" href="Section_start.html#start-6"><span class="std std-ref">-suffix command-line switch</span></a> when you invoke LAMMPS, or you can
use the <a class="reference internal" href="suffix.html"><span class="doc">suffix</span></a> command in your input script.</p>
<p>See <a class="reference internal" href="Section_accelerate.html"><span class="doc">Section_accelerate</span></a> of the manual for
more instructions on how to use the accelerated styles effectively.</p>
</div>
<div class="section" id="restrictions">
<h2>Restrictions</h2>
<p>This angle style can only be used if LAMMPS was built with the
USER-MISC package. See the <a class="reference internal" href="Section_start.html#start-2-3"><span class="std std-ref">Making LAMMPS</span></a>
section for more info on packages.</p>
<div class="admonition note">
<p class="first admonition-title">Note</p>
<p class="last">In the &#8220;Angles&#8221; section of the data file, the atom ID &#8216;j&#8217;
corresponding to the dipole to restrain must come before the atom ID
of the reference atom &#8216;i&#8217;. A third atom ID &#8216;k&#8217; must also be provided,
although &#8216;k&#8217; is just a &#8216;dummy&#8217; atom which can be any atom; it may be
useful to choose a convention (e.g., &#8216;k&#8217;=&#8217;i&#8217;) and adhere to it. For
example, if ID=1 for the dipolar atom to restrain, and ID=2 for the
reference atom, the corresponding line in the &#8220;Angles&#8221; section of the
data file would read: X X 1 2 2</p>
</div>
<p>The &#8220;newton&#8221; command for intramolecular interactions must be &#8220;on&#8221;
(which is the default).</p>
<p>This angle style should not be used with SHAKE.</p>
</div>
<div class="section" id="related-commands">
<h2>Related commands</h2>
<p><a class="reference internal" href="angle_coeff.html"><span class="doc">angle_coeff</span></a>, <a class="reference internal" href="angle_hybrid.html"><span class="doc">angle_hybrid</span></a></p>
<p><strong>Default:</strong> none</p>
<hr class="docutils" />
<p id="orsi"><strong>(Orsi)</strong> Orsi &amp; Essex, The ELBA force field for coarse-grain modeling of
lipid membranes, PloS ONE 6(12): e28637, 2011.</p>
<p id="allen"><strong>(Allen)</strong> Allen &amp; Tildesley, Computer Simulation of Liquids,
Clarendon Press, Oxford, 1987.</p>
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